1. Field of the Invention
The present invention relates to a tag communication device, a tag moving direction detecting system and a tag moving direction detecting method able to detect a moving direction of a moving body attaching a RFID tag thereto.
2. Background Art
A technique for sticking a RFID Radio Frequency Identification) tag to baggage and managing the baggage by performing wireless communication of this RFID tag and a reader-writer is recently used. In accordance with this technique, for example, data of ID (Identification), etc. can be automatically read from the RFID tag attached to the baggage conveyed by a belt conveyer, etc. Accordingly, a commodity distribution operation is efficiently intentionally performed. However, no detection can be performed for a conveying direction of this baggage. Therefore, a problem exists in that it is impossible to automatically detect whether it is warehousing or forwarding.
For example, there is a technique disclosed in JP-A-2005-345198 as a publicly known technique for solving such a problem. In the technique of this JP-A-2005-345198, for example, when a RFID tag 200 located in a position of FIG. 23A is moved until a position of FIG. 23B and a response signal from the RFID tag 200 becomes weak in a reader-writer 300, directivity of an antenna of the reader-writer 300 is controlled as shown in FIG. 23C. Namely, the beam of a radio wave radiated from the antenna of the reader-writer 300 is swung on both sides. A communication result with the RFID tag 200 at a swinging time of the beam of the radio wave onto one side, and a communication result with the RFID tag 200 at a swinging time of the beam of the radio wave on the other side are compared, and the moving direction of the RFID tag 200 is detected. Further, when there are plural RFID tags 200, the moving direction of each RFID tag 200 is detected by swinging the beam to each RFID tag 200 in time division.
However, in accordance with the technique of this JP-A-2005-345198, if the number of RFID tags 200 is increased, its processing becomes complicated and it becomes difficult to pursue the movement of each RFID tag 200. Further, when the RFID tag 200 is moved at high speed, it becomes difficult to again detect the position of the original RFID tag 200 while another RFID tag 200 is pursued. Otherwise, a problem exists in that it takes much time until detection even when this position is detected.